# Hurricanes – Why so fast Winds?

1. Jun 16, 2009

### Bjarne

Hurricanes – Why so fast Winds?

Which force is responsible for the very fast wind in a hurricane, and why is the fastest velocity close to the eye? – why not in the periphery ?

2. Jun 17, 2009

### turin

There are many forces. I would say, in a grand sweeping generalization, that the Coriolis force is responsible. However, I hate to call that a force, and prefer to call it the Coriolis effect. Another mechanism that must come into play is the pressure differential generated by the deviation from the Maxwell-Boltzman distribution in the atmospheric density, which is in turn caused by an anomolous temperature gradient.

Short answer: conservation of mass and momentum. The air flows into the eye, which has a smaller circumference that the outer edge. So, it gets squeezed in and travels faster. It's basically just a funneling (nozzling) effect. The same basic principle applies to putting your thumb on the end of the water hose to make the water squirt out faster.

3. Jun 17, 2009

### Bjarne

How?
I mean today the Coriolis force are there too.
But the clouds on the sky / wind are calm.

4. Jun 17, 2009

### DaveC426913

Wiki can provide a http://en.wikipedia.org/wiki/Hurricane#Mechanics".

Among other things, it points out that the Coriolis Effect is not the main source of energy; the main source of energy is the heat released from condensation of the rising moist air mass. The Coriolis Effect merely makes it spin.

Last edited by a moderator: Apr 24, 2017
5. Jun 17, 2009

### Bjarne

Sounds more logical yes...

BUT think about wind speed 300 Km/h or more
Hmmm..... energy from rising moist "only”?
It sounds to me like still some force is missing here.
Why this relative huge acceleration ??
I mean inner and outer diameter doesn’t make that much difference?

6. Jun 17, 2009

### DaveC426913

I'm thinkin' 300km/h winds is pretty tame considering the energy levels involved. It sucks the heat out of the ocean over thousands of square miles.

Of course it does. Watch water drain down the sink. The rotation at the centre is marked enough to actually create a funnel (water held against gravity by centrifugal force) compared to the outer edge, where the water might be almost still.

Last edited: Jun 17, 2009
7. Jun 17, 2009

### Bjarne

No doubt that the rising heat is parts of the force involved.
And no doubt it's a huge amount of energy involved....

BUT what make me wonder is relative slow raising heat ends up with huge wind velocity.
What exactly is responsible for such huge wind acceleration / velocity..?
I mean think about from the moment air begins to rotate slowly around a low pressure and then speed up day by day. Why this day by day increasing acceleration?

8. Jun 17, 2009

### DaveC426913

When ten cubic kilometres of air decides it wants to be five kilometres higher up in the atmosphere, then there's a ten cubic kilometre hole to fill in a hurry.

And it is a positive feedback cycle. The more air rises, the more wind; the more wind, the more evaporation; the more evaporation, the more energy.

9. Jun 17, 2009

### Bjarne

Yes it make sence.
Thank's

10. Jun 17, 2009

### granpa

what makes you think that the rising warm air is slow? the speed depends on the pressure difference and a 10 km high column of warm air can create quite a pressure difference.

11. Jun 17, 2009

### Bjarne

The confusion is properly that we do not know why a low pressure starts to rotate.
A hurricane (that reach USA) begins with very weak rotating thunder clouds near Africa.
It takes days before strong wind begins to occur.

Basically if the rotation would not occur, don’t you think it is difficult to imaging heat rising with 300 km/h?

I mean after the rotation has started it is easy to understand that we will have a self-perpetuating process.

12. Jun 17, 2009

### DaveC426913

We do know what causes the rotation - the Coriolis Effect. This effect occurs because the system is hundreds of miles across. And when you take a giant mass of air that's rotating at a slow, stately pace, and then compress it into a space that's one tenth or one hundredth the size (i.e. near the eye), the angular momentum is conserved, which means the slow stately winds will multiply ten-fold or a hundred-fold.

13. Jun 17, 2009

### LOKI777

it rotates because the earth rotates, winds are higher in the center because of the vacuum in the center, stronger and faster winds cause a smaller eye because of the squeeze.

14. Jun 17, 2009

### turin

Nice to see that you've come back around, Dave.

15. Jun 17, 2009

### DaveC426913

Come back around to what?

16. Jun 18, 2009

### Bjarne

This is both correct and false.

We do know the cause of the rotation when we speak about a certain size.

BUT when a small low pressure (and thunder clouds) begins to rotate (near by Africa) and travels over the Atlantic, the low pressure area are initially too small to that we can't blame the Coriolis force to be involved.

And the answer here is we do not know why small low pressures begins to rotate.

At least this is what was claimed at a scientific film I recently saw..

Last edited: Jun 18, 2009
17. Jun 18, 2009

### DaveC426913

It is still due to conservation of angular momentum. A draining sink does the same thing without benefit of Coriolis Effect.

18. Jul 1, 2009

### turin

It was a pun - apparently a bad one.

19. Jul 1, 2009

### turin

I would suggest the gigantic Atlantic anticyclone, generated from the Antilles high, that spurs off the huricanes that are ripe for the plucking from the Saharan rainstorms. The edge of the anticyclone pushes the rainstorms into an opposite rotation, like a sun gear causes planetary gears to spin in opposite directions.